Planting Logs to Grow … Soil

You may have noticed a cascade of “planted” logs in a front garden on Springdale Road (Druid Hills).We are using them to interrupt surface-water runoff, improve the soil, and hold water during drought. Because they are rather beautiful—gathering lovely moss and lichens—I also use them as a backdrop for planting perennials.

Colleague Walter Bland of Rock Spring Restorations first recommended this forestry technique (Log Erosion Barriers ) for a different project—steep, heavily wooded and scoured by runoff from lawns and gutters of uphill neighbors. (See Brookhaven Rain Garden). Since then, I’ve been using it on projects where the soil is steep or compacted. Because we are using it under living trees, however, we are setting them only shallowly into the soil. The logs are placed along the contours, perpendicular to water flow, capturing sediment and interrupting water channels, causing them to spread out into “sheet flow.”

The technique also reminds me of a permaculture technique called Hugelkultur, which echoes the natural decomposition occurring in forests. The logs not only look natural, they break down, adding badly needed fungi, organisms, organic material, and air pockets to the soil.

The Druid Hills property is not badly eroded nor is it steep; but the lawn is disappearing, the soil is compacted, and small water channels are developing.Shade and root competition from trees have likely played a major role in killing the fescue lawn, but there are probably other factors.

For one,Atlanta is getting hotter and drier, and fescue, which can take some shade, is neither heat nor drought tolerant. The loss of fescue has left the soil barer and smoother, increasing the speed of water runoff. Leaf blowing has likely contributed as well: blasts of hot air can bake the soil and kill plants; and leaf blowing removes leaves, which, ifleft on the ground, would break down, recycling nutrients and creating a spongier, more absorbent soil.

The logs will be a backbone to new plantings of native shade-tolerant grasses and perennials, mixed with some of the mosses.We will also be enlarging the “forest floor,”leaving more area for leaf fall. For more information, see “Druid Hills Woodland Glade.”

We urban folk do a terrific job—too good—of keeping our yards neat and tidy; carrying off the logs, leaves, and other debris that would naturally fall to the forest floor and replenish the soil.This was not a big deal when our metropolitan footprint was small compared to the extensive Piedmont forest surrounding us.

But our footprint is now enormous, and there are only pockets of that forest left in the metro Atlanta area—not enough to capture our water and revive our soils without a lot of help from us.